Open medicine (Warsaw, Poland) · 2026
Theoretical and experimental study on the cooling time of a single device after sterilization based on a zero-dimensional heat transfer model.
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Liu Zhili, Yang Haiyi, Chen Xiaoxuan, Ye Huamei, Wang Yuewei
Аннотация
OBJECTIVES: To establish a zero-dimensional heat-transfer model for an isolated single-sealed 316 stainless-steel cylindrical device after pressure-steam sterilization and to evaluate whether the 30-min cooling time required by national standards provides an adequate safety margin under controlled conditions.
METHODS: Ambient conditions of the sterile-material storage area were used as boundary conditions. Biot number analysis was used to confirm applicability of the lumped-capacitance model, and the governing equation was derived from Newton's law of cooling. Six 316 stainless-steel rods (diameter 4.5 mm, length 200 mm) were heated and cooled at 24 °C and 50 % relative humidity. Temperature was recorded every 5 s for 1,800 s, and each sample was tested three times. Cooling data were fitted with an exponential function in OriginPro.
RESULTS: The unadjusted theoretical model with h=5 W/(mˆ2 K) predicted 36.6 °C at 30 min, whereas the experimental fit approached ambient temperature and reached 24.6 °C. The fitted parameters were A=74.74 (95 % CI, 74.45-75.03), B=0.00402 sˆ-1 (95 % CI, 0.00399-0.00405), and C=24.56 °C (95 % CI, 24.53-24.59), with Rˆ2=0.9987 and a root mean squared residual of about 0.52 °C. The unadjusted theoretical curve is therefore a conservative reference rather than a point-accurate predictor.
CONCLUSIONS: For the tested simplified single device, cooling followed an exponential pattern, reached body-temperature level within about 7-8 min, and approached room temperature within about 16-20 min. The 30-min rule provides an adequate margin for this bounded scenario, but the findings should not be generalized to complex instruments, packages, multiple loads, or variable airflow conditions without further validation.
METHODS: Ambient conditions of the sterile-material storage area were used as boundary conditions. Biot number analysis was used to confirm applicability of the lumped-capacitance model, and the governing equation was derived from Newton's law of cooling. Six 316 stainless-steel rods (diameter 4.5 mm, length 200 mm) were heated and cooled at 24 °C and 50 % relative humidity. Temperature was recorded every 5 s for 1,800 s, and each sample was tested three times. Cooling data were fitted with an exponential function in OriginPro.
RESULTS: The unadjusted theoretical model with h=5 W/(mˆ2 K) predicted 36.6 °C at 30 min, whereas the experimental fit approached ambient temperature and reached 24.6 °C. The fitted parameters were A=74.74 (95 % CI, 74.45-75.03), B=0.00402 sˆ-1 (95 % CI, 0.00399-0.00405), and C=24.56 °C (95 % CI, 24.53-24.59), with Rˆ2=0.9987 and a root mean squared residual of about 0.52 °C. The unadjusted theoretical curve is therefore a conservative reference rather than a point-accurate predictor.
CONCLUSIONS: For the tested simplified single device, cooling followed an exponential pattern, reached body-temperature level within about 7-8 min, and approached room temperature within about 16-20 min. The 30-min rule provides an adequate margin for this bounded scenario, but the findings should not be generalized to complex instruments, packages, multiple loads, or variable airflow conditions without further validation.